1. Field of Invention
The present invention pertains to vehicle tire performance monitoring. In particular, the present invention pertains to monitoring slippage between a vehicle tire and a road or off-road surface.
2. Description of Related Art
Slippage between the tread blocks of a vehicle's tires and the surface upon which the vehicle is operating greatly affects overall tire and vehicle performance. For example, slippage of a tire against a road or off-road surface typically results in tire tread wear and a reduced operational life of the tire. Further, slippage of a tire against a road or off-road surface results in a loss of torque generated by the vehicle engine and power train, resulting in less efficient operation of the vehicle. Slippage also results in a loss of vehicle maneuverability in that a vehicle may fail to hold to the surface upon which the vehicle is operating, thereby causing the driver to limit the range of operational maneuvers performed in the vehicle. In a worst case scenario, slippage of one or more tires against a road or off-road surface can result in a loss of vehicle control which may result in an accident.
Unfortunately, accurate slippage information of a tire upon a road surface under a variety of operational and environmental conditions has, traditionally, been very difficult to obtain. One conventional approach is to place instruments within a test road surface itself. For example, one approach is to install within a test road surface a steel plate with a hole in the steel plate through which an instrumented needle protrudes above the surface of the plate. A test vehicle is driven along the test road surface and over the steel plate containing the instrumented needle. As a tire on the vehicle contacts the needle, the needle moves in the direction of slippage. A measure of the slippage may thereby be recorded by the needle's instrumentation.
One drawback associated with such an approach is that you can only collect data on a single point on the road surface and not on the tire itself. Therefore, although information is collected, it is unknown whether the information collected relates to a point at the front of the tire footprint or the back of the tire footprint. Such a drawback may be mitigated by using a plate that includes a matrix of instrumented needles. Although such an approach provides increased information over the footprint of the tire, the surface for which the measurements are collected remain measurements for slippage on the steel plate surface rather than the actual road surface. Further, it is difficult to use such an approach to determine slippage under a wide range of maneuvers due to the need to place one or more plates in a manner that allows the maneuver to be performed while the vehicle is over the steel plates. Still further, such an approach is not effective for measuring slippage under certain environmental conditions, such as snow, ice, and mud, nor can such an approach be used to measure slippage in off-road environments. In addition, efforts to collect slippage information using such instrumented plate techniques is typically very repetitious and time consuming. The results generated are often incomplete, error prone and/or ambiguous.